Starting a long dormant engine.

[Guest]

Well the time had finally come today to try and fire the 750 Kat engine. As documented in another thread it didn't start .

Now I reread all the threads on hard starting and just wanted to check something with you. The valves were adjusted when the head was put back on and the carbs were dipped and rebuilt (including o-rings). The battery is 2 years old out of the GS but is still strong. The starter does crank and there are clean plugs and they do spark. The only component missing is the airbox as I'm waiting for fresh boots.

Over and over, I've read that a proper sealing airbox is necessary for these bikes to run right but I've run other bikes without so I wonder will I not be able to even start it without an airbox? Am I wasting my time?

Wondering what the opinions are on this.

Cheers all,
Spyug

[hikermikem]

I don't think it will start without some restriction (airbox) on the intake side...

Some of these GS machines are super sensitive regarding the amount of air/restriction needed to properly make the carbs operate as intended.

For example, my '85 550L will not run if the seat is removed because the airbox snorkel is aligned with the seat underside to regulate the exact amount of air needed to mix in the carbs. If I put my hand over the snorkel intake the bike will run, remove it & the bike dies...

I believe Steve has posted that a clean shop rag draped over the carb intakes will usually provide enough restriction to get the bike running...

Maybe just use the old boots 'till ther new ones show up??

Good luck

[KitKat]

huh...

most of the threads i have read about not having the airbox on was that the bike ran crappy and died frequently, they were able to start it.

however, maybe your bike is super sensitive to its air... just another aspect of the bike's personality

[Nessism]

I'm pretty sure the bike should start, but run poorly without the airbox. Are you getting any fire at all? If not, did you pull a couple of plugs to see if they are wet? If the plugs are dry, open a couple of carb drain plugs to see if gas is inside.

One other thing to check is the cam timing. It's pretty easy to get the cams 180 degrees out (don't ask me how I know).

Keep going and you will figure it out.

[Ponderosa]

Long dormant

If I am firing a long dormant engine, I usually start by pulling the plugs, putting a little wd-40 in each cylinder, then spinning the engine until oil pressure is solid. Then put the plugs back in, hook all back up and fire at idle, it should idle if adjustment is close, vacum on most CV units between filter and carb enhances responsiveness, total performance.

[Octain]

When I was working on my 850 it wouldnt even start without the airbox.

Bad memory edit..
It did start but would only run for a few seconds on the first try. But after that it wouldnt unless the box was installed.

[old_chopper]

My 550 set for 24 years. I did a quick carb clean first to see if the engine was any good at all before spending any cash. It started after being "primed" with starting fluid but would barely run with no air box. The intake boots and o-rings were shot. It now has pods and drag pipes but I put a dynojet stage 3 kit in. It runs like a mad banshee!

[chef1366]

Compression, spark and gas is all you need.

[gs scott]

This past spring, I had to resort to some starting fluid sprayed into the airbox to help get my bike fired up for the first time. No air filter in place, but the box was connected to the carbs - fired up and ran fine. So, if you can at least get the old box on, might start easier.

[spyug]

Thanks for all the input guys.

Tried everything I could think of today including the Quickstart . Absolutely nothing even approximating trying to start.

Battery was fully charged and the starter cranks away. Voltage checks out at the coils and there is spark at each of the plugs. I can't check compression as I don't have an adapter to fit for my tester but there is compression when I hold my finger over the hole.

I even changed the carbs for a set that had worked on my GS. Still nothing, no bangs or backfires, spitting through the carbs nothing. On every other bike I've worked on, I've always managed to get some sign of life. Even with almost non existant compression.

This has got me baffled and all I can think of is I've got valve timing off but that seems unlikely as there no nasty sounds when I first turned the engine over after getting the head back on.

I guess I now might have to pop off the valve cover and see that things are lined up correctly and check that I set the valves properly. that and get a compression tester on it.

Any thing else I should be checking?

Cheers all,
spyug

[chef1366]

Nope, I would start with timing.
Cam and make sure you don't have the ignition timing off 180 degrees.

[Octain]

Before ya start taking stuff apart remove the plugs and spray a few skeets of gasoline into the chambers. Re-install the plugs and fire that beast up.
Like Chef said, fire, gas, and compression..

[spyug]

Thanks guys.

Tried all that stuff and as I said even tried quickstart (ether). Not even a hint of combustion.

Now I took off the valve cover and checked the timing marks. Everything is spot on. I checked the valve clearances and they are all around .12mm.

So now the only other thing is compression and I'll need to get a new fitting for my guage to test that.

Its truly confounding. I'm relatively new to bikes but I've built numerous 4, 6, and 8 cylinder engines including several race preps over the last 40 years so I'm somewhat experienced in getting things to fire. I can't remember ever having such a tough time with an engine.

Right now I'm scratching my bald head and the worst part is this will keep me awake all night until I figure it.

Stay tuned.

Cheers all,
Spyug

[KitKat]

have u checked your starting assembly?

does your starter gear and clutch engage?

maybe the starter gear isn't functioning properly?

[alke46]

I almost hate to suggest this but is the kill switch working like it should? I am sure you have not overlooked this though. Good luck.